Interference occurring due to transmissions sent from/to neighbor satellites, using the same frequencies as well as interference occurring due to communications transmitted along satellites beams using the same frequencies, tend to degrade the reception performance and to limit the maximal channel throughput.
Interference to communications exchanged along satellite links is one of the major factors limiting the capacity of satellite communication. Modern satellites include numerous transponders transmitting at different frequencies, different antennas (single beam or multiple beam), and different polarizations per antenna. Thus, a ground receiver of a satellite link is susceptible to interference that may arise, for example, from co-frequency transmissions at the same frequency, same beam but different polarization (co-frequency, co-beam, cross polarization), same frequency but a different beam (co-frequency, adjacent beam), and adjacent frequency channel from the same or from different beams.
As the satellite uplink receiver is also susceptible to interference, interference on the uplink may leak into the desired channel as well. Additionally, unwanted interference originating from an adjacent satellite may also occur as well as interfering signals from terrestrial sources.
Interference events may be caused by rules violations or errors made by operators. However, the effects of these events might be mitigated due to the newly established Carrier ID standard, which enables a satellite operator or regulators to identify and shut down interfering transmissions. Nevertheless, even links that operate in accordance with the operation rules and regulations may still be a source of interference.
Active interference cancellation means are available. Such means typically involve building a dedicated receiver to capture the interfering signal and then cancel it by subtraction from the wanted signal. Obviously, this technique is rather costly while perfect cancellation is never possible. Even when the interfering signal is known (which is the case when dummy frames are transmitted), cancellation requires synchronization and channel estimation of the interference, which might still require installation of additional circuitry.
A large part of the communication traffic transferred via satellites, is continuous in nature. It includes broadcast transmissions, distribution and contribution links, cellular and Internet connection backhaul traffic etc. The fact that the transmissions are continuous makes it possible to manufacture relatively simple receivers, which are not required to re-acquire and re-synchronize to separate transmission bursts. It also enables the receiver to track the various transmission parameters relatively in a straightforward operation. Hence, satellite communications' standards, such as DVB-S2 and DVB-S2X define a continuous transmission mode of operation in the forward link (transmissions being sent from the satellite(s) towards the terminals), and define that whenever the (hub) transmitter has no data to transmit, “dummy frames” will be transmitted. These dummy frames contain no information, create interference to adjacent beams and satellites, and as a result increase satellite power consumption.
However, not all of the traffic being exchanged, requires the use of strictly continuous links. Interactive communications for example, are bursty by nature, and an assembly of such links forms links of non-constant rate. Depending on the specific statistics of the link, there is always a difference between the allocated bandwidth of a link, which is typically determined by the difference between the peak information rate for transferring the information to the average information rate that can be supported. The dummy frames, used by the DVB-S2 and DVB-S2X standards, are used in order to compensate for this difference.